The danger of exposure to elevated levels of heavy metals, such as lead, in paint dust, contaminated soil, groundwater and water supplies, has been the subject of interest and global regulation for some time. Many developed countries have established regulatory limits to control the leaching of these inorganic contaminants into landfills or open environments where these wastes are disposed or reused. Heavy metal contamination may also occur at residential or commercial properties due to the original use of heavy-metal containing construction materials, such as lead-based paints, which flake or deteriorate to dust upon aging. Despite regulatory efforts, many sites of heavy metal contamination may be found in the United States and around the world.
Current Environmental Protection Agency (EPA) Renovation, Repair and Painting (RRP) rules recommend that dusts be minimized using wet scrape or wet sanding techniques. Using these techniques surfaces are wetted with water, then wetted dusts fall to the floor where they may be tracked around the work site or outside the work site. When the lead-based dusts become dry, they again become an inhalation hazard. Further, the water used to wet the dust and debris may suspend lead-based dust or paint chips containing lead and may become a source of contamination itself.
Efforts have been made to remediate heavy metals that leach into soil. For example, U.S. Pat. No. 5,162,600 teaches a process of contacting a phosphate-containing agent or a phosphite-containing agent with soil containing mobile lead. The lead reacts with the phosphate-containing or phosphite-containing agent to form immobilized, water-insoluble lead compounds. The '600 patent teaches loading the agent into the soil by spreading the composition over the surface of the contaminated site. Optionally, the agent may be plowed or disked into the soil to effect mixing.
The process of the '600 patent provides a method for reducing leachable lead in soil, but is expensive, time-consuming, labor-intensive, and may be impractical near trees, shrubby, flower beds, or buildings. In addition, the reactivity of phosphate-containing or phosphite-containing agents is related to the surface area of the agents. Certain phosphate compounds naturally form large agglomerates, which decreases the surface area of the compounds. Consequently, relatively large amounts of agglomerated phosphate-containing or phosphite-containing agents are needed for soil remediation.
The EPA has historically recommended measuring lead levels of painted surfaces using toxicity characteristic leaching procedure (TCLP) methods. Unfortunately, these methods are more suitable for measuring heavy metals of hazardous wastes going into landfills than for measuring levels in painted surfaces or in soils. Thus, these methods do not reflect the potential hazard from paint dusts and paint chips or in soils that may potentially be ingested, such as those heavy-metal contaminated sources found around homes, daycares or schools where children typically play. Recently, the EPA has started to use an in vitro bioaccessibility assay described in EPA 9200.1-86 November 2008 modified to pH 2.5 for a more accurate assessment of human risk from heavy metal presence.
The present invention provides a composition which, according to the new standards, renders a remediated surface or soil with substantially lower bioavailable lead than can be achieved from using prior art compositions. The composition is easy to apply to painted surfaces and soils, even when shrubbery and other plantings are present.